LaTeX.org

You can redefine the macro used by urldate:


\renewbibmacro*{urldate}{
(visited on \printfield{urlday}/\printfield{urlmonth}/\printfield{urlyear})
}


And you can change the sentence to Accessed: if you please.


\documentclass{article}
\usepackage[british]{babel}
\usepackage{biblatex ...